Fix `Text.Next.Account.new`

Motivation and Context

Running ligo run test mytest.mligo with a file mytest.mligo containing

let test_new =
  let acc = Test.Next.Account.new () in
  Test.Next.Address.get_balance acc.addr

yields an error

Error(s) occurred while checking the contract:
At (unshown) location 5, wrong stack type for instruction ADDRESS: [].

Description

We just add the missing IMPLICIT_ACCOUNT Michelson operation, and ligo run test mytest.mligo now returns

Everything at the top-level was executed.
- test_new exited with value 0mutez.

as expected.

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

Checklist:

• If a new syntax has been introduced, put a message on slack ligo-lsp
• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).